Memory devices may be provided in apparatuses such as computers or other electronic devices, including but not limited to portable memory devices, solid state drives, personal digital assistants, music players, cameras, phones, wireless devices, displays, chip sets, set top boxes, gaming systems, vehicles, and appliances. There are many different types of memory including random-access memory (RAM), read only memory (ROM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), flash memory, and resistance variable memory, among others.
Apparatuses, such as resistance variable memory devices, may be used as non-volatile memory for a wide range of electronic devices. Resistance variable memory devices may include, for example, phase change memory (PCM) or resistive memory (RR), among others. A physical layout of a PCM device may resemble that of a DRAM device where the capacitor of the DRAM cell is replaced by a phase change material, e.g., Germanium-Antimony-Telluride (GST) or other chalcogenide materials. That is, an access device such as a diode or metal oxide semiconductor field effect transistor (MOSFET) can be connected in series with the phase change material. Chalcogenide materials can include compounds of sulfides, selenides, or tellurides, among others. GST has been used in rewriteable optical discs, e.g., rewritable compact discs (CD-RW) and rewritable digital versatile discs (DVD-RW).
PCM may be written to change from a first state (e.g., logic “0”) to a second state (e.g., logic “1”) as with non-volatile memories. PCM may also be written to change from the second state to the first state. A conventional read operation to PCM is also similar to RAM. As such, PCM may be used in random-access memory. Write operations with PCM, however, are relatively slower than for conventional RAM. That is, time may be needed to manage and complete write operations, such as preparing data to be written to memory, suspending a write operation in case of a read access request, as well as to monitor the progress of a write operation. Read operations may be slower than for conventional RAM and read operations cannot be performed on a memory location that is involved in a concurrent write operation.
As a result of the limitations of using PCM as RAM replacement, operation of PCMs in memory systems is restricted in several ways. For example, write and read operations may not be performed at any time on any memory location. Status registers used for monitoring the progress of write operations may be regularly polled to determine completion of a write operation before starting a new write operation. Additionally, in some applications write operations are necessarily suspended for read operations and resumed upon completion of the read operation.